Aftermarket mufflers and engine damage?

[DarkLord]

Can anyone out there tell me if fitting an after market muffler on a bike means that you could run the risk of potential engine damage, as I keep getting different answers from different people.

I have a Hyo and apparently to fit the Screaming Demon mufflers on the Hyosungs, you don't need to have the carbies re-jetted.

I am wondering if the muffler has caused this in any way as another mate warned me about taking the stock muffler off the Hyosungs as that can cause engine damage, but then others say it's not a problem. I would like to fit a Screaming Demon on my Hyo, mainly because I'd like to have a little 250cc V-twin sprots bike that sounds like a Harley but I am not interested in putting one on if I am putting my engine at risk.

Also, will a free-flowing after market muffler help the performance of the bike at all as I have heard from some people that it will and from others that if it is free-flowing then there is no back pressure which will actually hinder the performance of the bike rather than help it.

Any help would be much appreciated!

Cheers all

DL

[vifferman]

If it is a well-designed muffler (and designed for the bike it's going on), then it can improve performance marginally, but only if (a) the exhaust it replaces is unnecessarily restrictive, and (b) the engine is tuned to the zorst (and vice-versa). At most, you're only going to reap maybe a couple of ponies.

Will it wreck the engine? Only of it makes the engine run very lean, and overheat. All you need to do to fix this (usually) is put a shim or two under the carb needles, or fit a larger diameter main jet.

The "back pressure" thing is to do with reflected pulses in the zorst at certain revs which help with some engines having valve overlap, where the intake and zorst are momentarily open at the same time. The 'back pressure' at the exhaust port helps with cylinder filling. In some circumstances, changing the exhaust can potentially cause overheating of the exhaust valves.

You need to ask yoursel if it is worth monkeying around with (and spending) good coin on summat that's really just "wank factor". Are you intending to keep the bike for a goodly long time? Is a Screaming Demon zorst going to get you more tickets for being non-standard/louder and result in more hassles at WOF time?

[DarkLord]

I guess you're right, Viffer. I do want to keep the bike for as long as possible. The only attractive thing about it really is the wank factor. I can see it being a hassle, WOF wise. I just find it confusing that people say that the Screaming Demon does not need a rejet yet people still do it.

I have heard that the Demon exhausts are specifically designed for the Hyosung though and unless you modify the airbox you don't need to rejet the carbs.

Is there any easy way to tell if the engine is running lean? I know it is running rich when it constantly reeks of petrol, idles really high and is backfiring but how do you tell if it is running too lean?

[jrandom]

... how do you tell if it is running too lean?

A conrod flying out through the side of the crank case is usually a good indicator.

[disenfranchised]

I've been running a SD exhaust on my Hyo for ages now...although I don't clock up K's as fast as some of the riders round here.

I haven't had anything done to the jets

I have asked my local bike shop to check the jets during a service and they said they were fine. General consensus seems to be that the bikes are designed to run a bit rich from the factory (possibly because of 88 octane rating petrol in asia) so the less restrictive exhaust leans it up a bit, but doesn't take it too far to cause issues.
Next service I'm sure I'll get those checked again.

I wouldn't say that I can really notice any performance difference since I've had it fitted...maybe when I first put it on I thought it felt like it picked up a bit faster....now the whole bike feels slow however (time to get that full license and upgrade)

I don't think these mufflers are that "designed" specifically for the hyo.
SD made identical looking mufflers for CBR..and the only thing you could see that was different was the bolt pattern.

I wouldn't be surprised if it's just a generic muffler tube from china, that SD put the flange on, and a badge and then resell.

I don't regret buying it though...it certainly makes the bike sound like I wanted it to.

Oh...and I've never had a WOF problem either...the shop has commented on how it's louder than stock, but still fine.

So i'd say, if you want one get it....you can always keep the stock muffler in case you want to go back.

[DarkLord]

A conrod flying out through the side of the crank case is usually a good indicator.

Haha, Very helpful. Cheers

[DarkLord]

I've been running a SD exhaust on my Hyo for ages now...although I don't clock up K's as fast as some of the riders round here.

I haven't had anything done to the jets

I have asked my local bike shop to check the jets during a service and they said they were fine. General consensus seems to be that the bikes are designed to run a bit rich from the factory (possibly because of 88 octane rating petrol in asia) so the less restrictive exhaust leans it up a bit, but doesn't take it too far to cause issues.
Next service I'm sure I'll get those checked again.

I wouldn't say that I can really notice any performance difference since I've had it fitted...maybe when I first put it on I thought it felt like it picked up a bit faster....now the whole bike feels slow however (time to get that full license and upgrade)

I don't think these mufflers are that "designed" specifically for the hyo.
SD made identical looking mufflers for CBR..and the only thing you could see that was different was the bolt pattern.

I wouldn't be surprised if it's just a generic muffler tube from china, that SD put the flange on, and a badge and then resell.

I don't regret buying it though...it certainly makes the bike sound like I wanted it to.

Oh...and I've never had a WOF problem either...the shop has commented on how it's louder than stock, but still fine.

So i'd say, if you want one get it....you can always keep the stock muffler in case you want to go back.

Thanks. Have you had any trouble with the regarding the noise of it?

[vifferman]

Is there any easy way to tell if the engine is running lean? I know it is running rich when it constantly reeks of petrol, idles really high and is backfiring but how do you tell if it is running too lean?

Ah - you're not quite right there! And the "reeks of petrol" and "high idle" apply only when running on the idle jet anyway.
If it's running lean, it will pop and backfire on the overrun (closed throttle), and run a little hotter. It will run better when hot than when cold. On a constant throttle opening, it may exhibit a "lean surge" - a rhythmic surging where it slows and speeds up very slightly.
If it's too rich, the bike will run better when cold and get worse when it heats up. If it's a rich idle problem, then when you blip the throttle, it will speed up, then the revs will drop below idle, then creep up to idle again.

Here's summat that will help; otherwise google "motorcycle carb tuning".

[TripleZee Dyno]

Can anyone out there tell me if fitting an after market muffler on a bike means that you could run the risk of potential engine damage, as I keep getting different answers from different people.

I have a Hyo and apparently to fit the Screaming Demon mufflers on the Hyosungs, you don't need to have the carbies re-jetted. However Gubb, as many of you may know, had a Screaming Demon on his, with a modified air box and re-jetted carbies, and his engine blew a piston in the front cylinder.

I am wondering if the muffler has caused this in any way as another mate warned me about taking the stock muffler off the Hyosungs as that can cause engine damage, which seems to be what happened to Gubb's bike. I would like to fit a Screaming Demon on my Hyo, mainly because I'd like to have a little 250cc V-twin sprots bike that sounds like a Harley but I am not interested in putting one on if I am putting my engine at risk.

Also, will a free-flowing after market muffler help the performance of the bike at all as I have heard from some people that it will and from others that if it is free-flowing then there is no back pressure which will actually hinder the performance of the bike rather than help it.

Any help would be much appreciated!

Cheers all

DL

If you were to change mufflers we could run the bike up on our dyno and give you a definitive answer as to whether its running rich lean or indifferent.
Its not free, costs $120, but you will know whats happening with your bike.
You wont have to lay awake at night wondering, shall I, should I, what if, oh no,
If it does need rejetting/tuning we can handle that for you as well, or point you in the right direction if you wish to do it yourself.
Personal opinion, put a muffler on and enjoy yourself
cheers

[TripleZee Dyno]

A conrod flying out through the side of the crank case is usually a good indicator.

Hi Dan
did you see this chart comparing your GSX1400 to an M109?
http://www.kiwibiker.co.nz/forums/sh...t=88482&page=4

[jrandom]

Hi Dan
did you see this chart comparing your GSX1400 to an M109?
http://www.kiwibiker.co.nz/forums/sh...t=88482&page=4

I did! Spooky innit, for two such apparently different engines.

[FROSTY:Me]

Now i DONT know for sure if Hyo's are the same as suzuki's as far as exhausts effect on performance and jetting.
On my SV650 changing the muffler did FSA to performance and on the dyno nada effect on fuel flow either.
But then I put the M4 Headers and link pipes on as well. Suddenly a dramatic change and jetting changes needed to suit.

But Most important was the way I found out and that was by doing a dyno run after each change.
To me unless you KNOW that you need a certain sized main because italready been done then a dyno run is really cheap insurance

[DarkLord]

So I'm kind of a mechanical n00b, but after much scouring of Wikipedia, this is a brief summary of what I have learned on the subject -

(feel free to correct me if I am wrong of course)

Putting an after market muffler on the bike (without changing the header pipes or anything) should not affect the performance and you should not have to rejet. The way the carburettor works is that it takes in air through the airbox and takes fuel from the gas tank. It then mixes them together and they go into the engine.

If I change the airbox so it lets in more air then the carburettors will need to have the fuel jets replaced, I'm assuming to jet more fuel into the carburettors. Otherwise, without re-jetting the carburettors and modifying the airbox, the engine will be running too lean (not enough fuel in the mix) and this can cause major mechanical problems. But, if I leave the airbox alone and all of the header pipes from the cylinders intact, I should be ok to replace the muffler as this will not affect the fuel/air mix in the engine and so should not put the engine at risk.

Am I right with this?

[tri boy]

Pretty good summary there.
I havn't seen any 250GTR's with faults related to the SD muffler.
Nice unit IMHO.
Most of the tuning related with exhausts is in the header length, (ranging from about 24-30inches).
You should be fine with the muffler. A fuel/air mix gauge can be plumbed into header pipes to read the mix. (about 13:1 is ball park), but an adapter has to be welded into a pipe.
Dyno runs are probably your best bet for a relaxed state of mind.

[TripleZee Dyno]

So I'm kind of a mechanical n00b, but after much scouring of Wikipedia, this is a brief summary of what I have learned on the subject -

(feel free to correct me if I am wrong of course)

Putting an after market muffler on the bike (without changing the header pipes or anything) should not affect the performance and you should not have to rejet. The way the carburettor works is that it takes in air through the airbox and takes fuel from the gas tank. It then mixes them together and they go into the engine.

If I change the airbox so it lets in more air then the carburettors will need to have the fuel jets replaced, I'm assuming to jet more fuel into the carburettors. Otherwise, without re-jetting the carburettors and modifying the airbox, the engine will be running too lean (not enough fuel in the mix) and this can cause major mechanical problems. But, if I leave the airbox alone and all of the header pipes from the cylinders intact, I should be ok to replace the muffler as this will not affect the fuel/air mix in the engine and so should not put the engine at risk.

Am I right with this?

That is a fairly simplistic explanation and while not exactly wrong its not exactly right either. There is no right or wrong answer. Its a bit like asking someone "how long is a piece of string?" All answers will be right and wrong to a lesser or greater degree at the same time.
The thing that will wreck the engine isnt the lean mixture but excessive heat your engine cant get rid of. Heat is a by product of combustion, HP is also a by product of combustion. Good combustion produces a certain amount of heat/HP, poor combustion produces more heat/HP, (or less)
eg Cruising at 120k, a bike may need 20hp. A lean 20hp may be equivalent to a normal mixtures 30hp worth of heat. A 100hp engine no problem because although it is running hotter than it should it is well within the capabilities of the engines cooling system.
A 35hp engine on the other hand is in the upper ranges of its capabilities.
Crack both bikes along at 150k and if an engine is going to blow it will be the small one. Why? because although you may need 35hp to do 150k you are producing 60hp worth of heat. the big bike no problem, the little bike is probably beyond its design limits for the cooling system. Keep it up and sooner or later it will go pop. Small engines have to work harder to do the same things as a big engine, and so they are usually operated closer to their limits more often than a big engine.

Put your muffler on, dont tune, will it do any damage? who knows? nobody knows. You wont know until you do it.
Depends a lot on how you ride it. Dont give it more than half throttle, dont go over 100k you will "probably" be OK.
You could put "bigger" jets and a washer under the needles and it wont run lean but likely you will lose power and it wont be running as good as it should be. On a 250 you dont have such an excess of HP that you can afford to throw away 3-4.
Best bet is get it checked, preferably on a dyno. The dyno will load the bike under controlled conditions, mixture and temperatures monitored so that even if it is running dangerously lean it will be picked up in a few seconds.
At the end of the day you can have 100 opinions but you still wont actually be any better off.

This is also a generalised simplistic explanation and may or may not apply to your bike, but the general principles apply to most engines more or less depending how long a piece of string is
Good Luck